An RTP (Real-time Transport Protocol) is used as a protocol to transmit/receive real-time data such as Audio and Video on an IP network (NPLT 1). The RTP includes an RTP control protocol (RTCP) as a control protocol. In consideration of scalability in terms of the number of terminals participating in an RTP session, the RTCP is designed such that consumption of public network resources by overhead of control for data transfer is minimized (NPLT 2). For example, a receiver report (RR) is data that is statistically processed based on received data for a predetermined period, and a transmission frequency of the RR is limited.
In recent years, with an increase in speed of a network configuration line and diversification of usage patterns such as use of an Internet protocol group such as an RTP/RTCP in a private system and use of the Internet protocol group in a mobile system, retransmission can be applied to a kind of control feedback of an RTP serving as an extension (NPLT 3, NPLT 4, and NPLT 5). In this manner, the retransmission can be requested on a granularity in units of RTP packets (sequence numbers) constituting the real-time data.